The moons telesto and calypso, orbiting at the lagrangian points of saturn and the moon tethys,

Tethys orbits Saturn in an almost perfectly circular orbit with a radius of 294,619 km (183,000 miles), taking 45.3 hours to complete one orbit.  It is roughly spherical, about 1,066 km (670 miles) across.  Tethys has a number of interesting surface features, the most obvious being Odysseus, a huge crater 400 km (250 miles) across. Features on Tethys are named for characters and places from The Iliad and The Odyssey.  As Tethys comprises principally water ice, the crater has slumped over eons and has lost the ring of mountains around it, and the central peak, typical of impact craters.  Penelope is another large crater with, to its left, three smaller features all about the same size that run north to south, top to bottom in the image of Penelope, below.  They are called, from top to bottom, Phemius, Polyphemus and Ajax.Another large feature is the Ithaca Chasm.  It is 2,000 km (1,250 miles) long, 100 km (62miles) wide and 3 to 5 km (2 to 3 miles) deep.  As the internal liquid water froze, it would have expanded, and probably cracked the surface that had already frozen over.  It is also possible that it is a crack resulting from the impact that caused the Odysseus crater. 

In the images to the right, you see the Ithaca Chasm running from the upper right to lower left. 

Tethys

Solar System -

Calypso

Telesto

Image Credit: NASA/JPL/Space Science Institute (Cassini)

Odysseus Crater

Penelope Crater

Telesto and Calypso, two of Saturn's smaller moons, are in the same orbit as Tethys, but in its L4 and L5 Lagrangian points.  They were both first observed in 1980.  Telesto orbits Saturn in Tethys' L4 which is 60º ahead of Tethys.  It has an elongated shape with dimensions of 32.6×23.6×20 km, giving an average diameter of 24.8 km. 

Calypso orbits in the L5, 60º behind Tethys.  It is also elongated in shape, like Telesto, but somewhat smaller at 30.2×23×14 km, giving an average diamter of 21.4 km

Saturn's moons are grouped as follows.  Select to see details of the moon or the group of moons:

Mimas • Enceladus • Tethys • Dione • Rhea • Titan • Iapetus • Hyperion • Norse Grp • Shepherd Moons • Alkyonides • Inuit Grp • Gallic Grp • Misc

Tethys ( “TEE this”  ) is the ninth of Saturn’s known satellites:

In Greek mythology Tethys was a Titaness and sea goddess who was both sister and wife of Oceanus.

Discovered by Cassini in 1684.

Tethys’ low density indicates that it is almost completely composed of water ice, similar to Dione and Rhea.

The western hemisphere is dominated by a huge impact crater, called Odysseus, whose 400 km diameter is nearly 2/5 of that of Tethys itself (right). That such an impact didn’t shatter Tethys completely indicates that it may have been liquid or at least not very solid at the time. The crater is now quite flat (or more precisely, it conforms to Tethys’ spherical shape), like the craters on Callisto, without the high ring mountains and central peaks commonly seen on the Moon and Mercury.

The second major feature seen on Tethys is a huge valley (called Ithaca Chasma) 100 km wide and 3 to 5 km deep which runs 2000 km or 3/4 of the way around Tethys’ circumference (above).

Clearly then, Tethys has not always been frozen solid. At some point in its past it was probably liquid. The impact craters from that era have been smoothed out. As it froze and expanded, the surface must have cracked to accommodate the extra volume producing Ithaca Chasma. The smaller impact craters we see today are more recent.

There are no albedo features on Tethys as there are on Rhea and Dione.

Telesto and Calypso orbit in Tethys’ Lagrange points (60 degrees ahead and behind Tethys in the same orbit).

More about Tethys

Telesto

Saturn XIII

Telesto (“tah LESS toh”) is the tenth of Saturn’s known satellites:

In Greek mythology Telesto was a daughter of Oceanus and Tethys.

Discovered by Smith, Reitsema, Larson and Fountain in 1980 from ground-based observations.

Telesto is in Tethys’ leading Lagrange point.

Calypso

Saturn XIV

Calypso (“ka LIP so”) is the eleventh of Saturn’s known satellites:

In Greek mythology Calypso was a sea nymph who delayed Odysseus on her island for seven years.

Discovered by Pascu, Seidelmann, Baum and Currie in 1980 from ground-based observations with prototype cameras destined for the HST.

Calypso is in Tethys’ trailing Lagrange point.

Calypso and Telesto are among the smallest moons in the solar system.

Note: the pictures of Calypso on the Voyager CD-ROMs are mislabeled; they’re really pictures of Prometheus. Similarly, the pictures labeled Telesto are really pictures of Pandora. The only real pictures of Calypso and Telesto are the ones above (until Cassini arrives 🙂

More about Telesto and Calypso

Open Issues

• How did Telesto and Calypso end up in the Lagrange points? Are they remnants of a collision?

Telesto /təˈlɛstoʊ/ is a moon of Saturn. It was discovered by Smith, Reitsema, Larson and Fountain in 1980 from ground-based observations, and was provisionally designated S/1980 S 13.[4] In the following months, several other apparitions were observed: S/1980 S 24,[5] S/1980 S 33,[6] and S/1981 S 1.[7]

Telesto

Telesto as seen by the Cassini probe in October 2005

DiscoveryDiscovered by

• Bradford A. Smith
• Harold Reitsema
• Stephen M. Larson
• John W. Fountain

Discovery dateApril 8, 1980Designations

Designation

Saturn XIIIPronunciation/təˈlɛstoʊ/

Named after

Τελεστώ Telestō

Alternative names

Tethys B
S/1980 S 13AdjectivesTelestoan /tɛləˈstoʊ.ən/ or Telestoian /tɛləˈstoʊ.iən/Orbital characteristics

Semi-major axis

294619 kmEccentricity0.000

Orbital period (sidereal)

1.887802 d [1]Inclination1.19° (to Saturn's equator)Satellite ofSaturnGroupL4 Tethys trojanPhysical characteristicsDimensions32.6±1.0 km × 23.6±0.6 km × 20±0.6 km [2]

Mean radius

12.4±0.4 km [2]

Synodic rotation period

synchronous

Axial tilt

zero

Apparent magnitude

18.7 [3]

In 1983 it was officially named after Telesto of Greek mythology.[a] It is also designated as Saturn XIII or Tethys B.

Telesto is co-orbital with Tethys, residing in Tethys' leading Lagrangian point (L4). This relationship was first identified by Seidelmann et al. in 1981.[8] Another moon, Calypso, resides in the other (trailing) Lagrangian point of Tethys, 60 degrees in the other direction from Tethys. The Saturnian system has two additional trojan moons.

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